The impact of gyrB and eis mutations in improving second-line drug resistance detection among Mycobacterium tuberculosis isolates from Georgia [PublishAheadOfPrint]

SETTING: The country of Georgia has a high burden of multi- and extensively drug-resistant tuberculosis (XDR-TB).

OBJECTIVE: To evaluate whether the detection of mutations in gyrB and eis genes increased the sensitivity of detecting phenotypic resistance to ofloxacin and kanamycin or capreomycin as compared to use of the first generation MTBDRsl assay alone which evaluates for mutations in gyrA and rrs genes.

DESIGN: A retrospective study of storedMycobacterium tuberculosis isolates. All isolates underwent DNA sequencing of resistance determining regions.

RESULTS: Among 112 M. tuberculosisisolates with DNA extraction, targeted sequencing was successfully performed for each gene as follows:gyrA – 98%; gyrB – 96%; rrs – 93% and for the eis gene and its promoter - 93%.The specificity and hence positive predictive value ofgyrA and gyrB mutations for detecting ofloxacin resistance were 100%. The addition of gyrB mutations increased the sensitivity of phenotypic ofloxacin resistance detection by 13% (75 to 88%).All rrs resistant conferring mutations were A1401G and this mutation had a low sensitivity (40% and 18%) and high specificity (95% and 100%) in predicting phenotypic capreomycinand kanamycin resistance, respectively. The eisC-14T mutation increased the sensitivity of phenotypic kanamycin resistant by 9% (18 to 27%) and was found solely in kanamycin phenotypic resistance isolates.

CONCLUSIONS: Our data showed that the inclusion of eis C-14T and gyrB mutations in addition to mutations rrs and gyrAgenes improves the sensitivity of phenotypic ofloxacin and kanamycin resistance, respectively.

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